1. Field of the Invention
This invention relates to the field of caging systems for free gyroscopes.
2. Prior Art
Various types of caging system are commonly used for free gyroscopes to align the inner and outer gimbals thereof to a predetermined position with respect to the gyroscope frame or case. For the gyros used in missiles and thus intended for one time use only, pyrotechnic devices are frequently used which, when fired, move the caging mechanism from a preset caged condition. Also used are solenoid actuators, particularly for gyros for aircraft which will be repeatedly used, as the solenoid actuators may be operated over and over again as required.
Pyrotechnic devices, when usable, have the advantage of low cost, though have the disadvantage that the device, being usable only once, cannot be tested. Solenoid actuators, on the other hand, while being readily testable and repeatedly usable, have certain characteristics which tend to affect reliability in an adverse manner. By way of example, solenoid devices exhibit a very nonlinear force versus position characteristic, having a minimum pull at the start of actuation and a pull force which may be many times greater at the end of the actuation. Solenoid devices also dissipate substantial power and heat, if energized for substantial periods. Accordingly, when used as the driving force for caging mechanisms, solenoids commonly utilize a mechanical latch to keep the solenoid latched without the continuous application of power, with a spring linkage driving the caging mechanism. The mechanical complexity, the requirement of a second solenoid to release the mechanical latch, the nonlinear forces of both the solenoid and a spring linkage and wear associated therewith tend to limit the life and reliability of such systems.